1. Field of the Invention
The present invention relates to vibrating gyroscopes and, more specifically, it relates to vibrating gyroscopes for use in camera-shake corrections, navigation systems, vehicle-posture control, and the like.
2. Description of the Related Art
FIG. 10 is an illustration showing an example of a conventional vibrating gyroscope 1. The vibrating gyroscope 1 includes a rectangular-parallelepiped vibrator 2. The vibrator 2 is formed by laminating two planar piezoelectric members 3a and 3b. The piezoelectric members 3a and 3b are polarized in directions opposing each other. Between the piezoelectric members 3a and 3b, an intermediate electrode 4 is formed. In addition, on one main surface of the piezoelectric member 3a, detection electrodes 5a and 5b, which are two-split parts, are formed. Furthermore, on the entire other main surface of the piezoelectric member 3b, a drive electrode 6 is formed.
In order to use the vibrating gyroscope 1, the detection electrodes 5a and 5b are connected to an adding circuit 7. The adding circuit 7 is connected to a gain control circuit (AGC circuit) 8. The AGC circuit 8 is connected to a phase circuit 9. A signal output from the phase circuit 9 is input to the drive electrode 6. The adding circuit 7, the AGC circuit 8, and the phase circuit 9 form a drive circuit. In addition, the detection electrodes 5a and 5b are connected to a differential circuit 10. The differential circuit 10 is connected to a synchronous detection circuit 11. A signal output from the differential circuit 10 is detected in synch with the signal of the AGC circuit 8. In addition, The synchronous detection circuit 11 is connected to a smoothing circuit 12, which is connected to a DC amplifying circuit 13.
In the vibrating gyroscope 1, by vibration of the vibrator 2, signals output from the detection electrodes 5a and 5b are added by the adding circuit 7, and the added signal is amplified by the AGC circuit 8 so as to make the amplitude of the signal constant. After this, the amplified signal is phase-adjusted by the phase circuit 9. The driving signal obtained in this way is input to the drive electrode 6, whereby the vibrating gyroscope 1 is self-excited. As a result, the vibrator 2 performs bending-vibration in a direction orthogonal to the drive electrode 6.
From the detection electrodes 5a and 5b, signals in accordance with the bending-vibration of the vibrator 2 are output. When the vibrating gyroscope 1 does not rotate, the bending conditions of the parts where the detection electrodes 5a and 5b are formed remain unchanged. Thus, the same signal from each of the two detection electrodes 5a and 5b is output. Therefore, the output of the differential circuit 10 becomes zero. When a rotation angular velocity is added around the center axis of the vibrator 2, Coriolis force causes a difference in the bending-vibration conditions between the part where the detection electrode 5a is formed and the part where the detection electrode 5b is formed. As a result, the detection electrodes 5a and 5b output different signals. Thus, the differential circuit 10 outputs a signal in accordance with the difference between the signals output from the detection electrodes 5a and 5b. After the signal is detected by the synchronous detection circuit 11 and smoothed by the smoothing circuit 12, the signal is amplified by the DC amplifying circuit 13, with the result that a DC signal in accordance with the rotation angular velocity can be obtained. Therefore, by measuring the signal output from the DC amplifying circuit 13, the rotation angular velocity added to the vibrating gyroscope 1 can be detected.
Regarding the use of the vibrating gyroscope 1, when a reference potential is used to secure a stable operation, the intermediate electrode 4 disposed between the piezoelectric members 3a and 3b is connected to the reference potential.
An equivalent circuit for representing the driving detection circuit of the vibrating gyroscope 1 is a circuit as shown in FIG. 11. In this equivalent circuit, the symbol Vdrv denotes a circuit driving voltage, the symbol Rd denotes a drive resistance, the symbol Z denotes a vibrator characteristic impedance, the symbol Rs denotes a detection resistance, and the symbol Vs denotes a detection voltage. As shown in the equivalent circuit, the detection voltage Vs is determined by the partial-potential ratio between Rd, Z, and Rs. However, when the values of Rd, Z, and Rs change due to changes in external environments and changes with the elapse of time, the value of Vs also changes. Thus, when changes in the detection voltage occur due to changes in the external environments and changes with the elapse of time, a rotation angular velocity cannot be accurately detected.
In addition, when the intermediate electrode is connected to the reference potential to secure a stable operation, it is necessary to lead out a wiring pattern from the intermediate electrode. However, in order to lead out the wiring pattern from a thin intermediate electrode, the structure must become complicated, with the result that having such a structure is not advantageous in terms of processing accuracy and cost.
Accordingly, it is an object of the present invention to provide a vibrating gyroscope capable of being connected to a reference potential with a simple structure and suppressing changes in a detection signal due to changes in external environments and changes with the elapse of time.
The present invention provides a vibrating gyroscope including a vibrator on which a plurality of piezoelectric members polarized in directions opposing each other is laminated, at least one drive electrode formed on one of the mutually opposing main surfaces of the vibrator to input a signal for exciting the vibrator, at least two detection electrodes formed on one of the mutually opposing main surfaces of the vibrator to output a signal in accordance with vibration of the vibrator, and at least one reference electrode formed on one of the mutually opposing main surfaces of the vibrator to be connected to a reference potential. In this vibrating gyroscope, the reference electrode is formed in a position opposing the drive electrodes and the detection electrodes.
In this vibrating gyroscope, the drive electrodes and the detection electrodes may be formed on the same main surface of the vibrator or may be formed on different main surfaces of the vibrator.
Furthermore, the detection electrodes may be connected to a charging amplifier for converting a generated charge into a voltage to detect a rotation angular velocity input from a differential signal of the output of the charging amplifier.
By connecting the reference potential formed in the position opposing the drive electrodes and the detection electrodes to the reference potential of the driving detection circuit, electrical isolation between the driving side and the detecting side can be facilitated. As a result, influence of changes in the drive resistance of the driving side becomes less. Additionally, a signal-detection reference can be defined so that accurate signal detection can be performed. As a result, the condition of a vibrator like the AGC circuit can be accurately monitored.
Furthermore, since the input impedance of the charging amplifier for converting changes in a charge into a voltage is zero, by connecting the detection electrodes to the charging amplifying, the voltage of the detection signal is not influenced by the characteristic impedance of the vibrator. Thus, changes in the vibration of the vibrating gyroscope according to the rotation angular velocity can be accurately detected.
According to the present invention, the reference electrode is disposed on either one of the main surfaces of the vibrator in such a manner that the reference electrode is opposed to the drive electrodes and the detection electrodes, and the reference electrode of the vibrating gyroscope is connected to the reference potential. With this arrangement, since there is less influence from the changes in circuit impedance due to the changes in external environments and changes with the elapse of time, a rotation angular velocity can be accurately detected. In addition, since the reference electrode is formed on the main surface of the vibrator, the reference electrode can be easily connected to the reference potential. As a result, when compared with the conventional gyroscope in which an intermediate electrode is used as a reference electrode, the gyroscope of the present invention is more advantageous in terms of processing accuracy and cost.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.